In the intravenous administration of medical liquids to a patient, it is often desired to administer more than one medical liquid through a single venous puncture site. For example, a container of dextrose or saline solution may be administered through a parenteral administration set such as sold by Travenol Laboratories, Inc. of Deerfield, Illinois, identified as a CONTINU-FLO.RTM. set, such as Product Code Nos. 2C0123 and 2C0251. The downstream end of the administration set is connected to a venous catheter, such as a FLASH-CATH.RTM. catheter sold by Travenol Laboratories, identified by Product Code No. 2N1175.
A second medical liquid, in another source container, may be infused through the same puncture site and venous catheter by connecting the second container to a secondary medication administration set such as identified by Product Code No. 2C0418, sold by Travenol Laboratories. The other end of the secondary medication set has a needle which is inserted into an injection site on the primary CONTINU-FLO set.
Another system designed for the infusion of two medical liquids has been sold by Abbott Laboratories.
The advantage of such systems for infusing two medical liquid sources is that only a single entry point is made into the patient. Further, the nurse or other medical personnel need not engage in the time consuming task of finding another access vein for puncture. Thus, the above-described system reduces patient trauma, reduces the chance of patient infection and saves valuable time of medical personnel. A system such as described above is shown in FIG. 1.
In U.S. Patent Nos. 4,034,754 and 4,105,029 there is shown another system for the sequential administration of two medical liquids. There, the first medical liquid is delivered to a drip chamber through a drop former having a restricted lumen as compared to the drop formers in the administration set referred to above by product codes. Such a restricted lumen drop former increases the drop rate in the drip chamber, which a nurse uses to determine flow rate. Some nurses prefer a higher drop rate in order to make a quicker, more accurate determination of flow rate. This is especially true where two or more medical liquid sources are being used because one liquid source, such as a dextrose or saline solution, may be delivered at a slow rate such as, for example, 60 ml per hour, to simply keep the vein open for the addition of further medication from a second solution container.
The restricted drop former does, however, make this system suseptible to development of a suction pressure head in the tubing downstream from the drip chamber, especially when a higher fluid flow rate of the second liquid source is desired. The '754 and '029 patents disclose a solution to this problem, whereby constricted lumen tubing is employed downstream of the tubing set connection leading to the secondary medical liquid source. The downstream constricted-lumen tubing reduces the suction pressure head and eliminates the problem of drawing air through the tubing into the patient's venous system.
In each of the systems described above, the secondary medical liquid container is disposed at a higher elevation than the first liquid container. Since it has a higher upstream pressure, or head, the secondary liquid is delivered upon opening of its associated flow path, stopping delivery of the first solution. After the second medical liquid is delivered, the first medical liquid again begins to flow, keeping the patient's vein open.
One disadvantage to these systems is that the flow rates of the first and second medical liquids cannot be independently controlled. For instance, the second medical liquid is most often delivered at a higher flow rate than the first medical liquid, such as, for example, 300 ml per hour. After the second medical liquid is delivered, the first medical liquid is delivered at the same higher rate at which the second medical liquid had been delivered. Although not typically posing a danger to the patient, the first medical liquid such as dextrose or saline solution will then be rapidly infused in the patient. The nurse must therefore monitor the system fairly closely so that he or she may reduce the flow rate of the first liquid after the second liquid is delivered or else return to the patient's bedside before the first solution container is emptied in order to replace that container.
If the first medical liquid is entirely delivered before the nurse returns there is a strong possibility that the accessed peripheral vein will collapse. While not dangerous, this situation will necessitate making another venous puncture for delivery of further medical liquid.
Various attempts have been made to develop systems for the independently controlled sequential administration of two medical liquids, so that upon exhaustion of the second liquid source the first source will flow at the pre-selected slower flow rate. Such systems are shown, for example, in U.S. Pat. Nos. 4,219,022; 4,236,515; 4,258,712; 4,237,880; 4,250,879; 4,252,116; 4,256,104; 4,256,105; and 4,324,238.
These disclosures are all directed toward systems to enable independently controlled flow rates from two separate medical liquid sources. All are directed toward systems which include an air barrier and/or a liquid sequencing valve of somewhat complex construction. At least some of the systems shown in these patents, such as shown for example, in U.S. Pat. No. 4,256,104, include a critical failure mode inherent in the system configuration. Stated differently, upon failure of the air barrier means, such as caused by a pin hole size leak in a hydrophillic filter membrane, all protection against patient air embolism is lost and air will in all likelihood be forced into the patient, due to factors such as a large remaining head pressure upstream of the air source and a large suction head pressure downstream of the air source. The failure mode is critical because failure of the system is likely to result in serious patient injury or death.